package com.click369.mianshiqingbao.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

public class SnowflakeIdWorker {
    private static final Logger logger = LoggerFactory.getLogger(SnowflakeIdWorker.class);
    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 10; //序列号占用的位数
    private final static long MACHINE_BIT = 5;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    public final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    public final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;  //数据中心
    private long machineId;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳
    /**
     * 根据MAC生成datacenterId，根据MAC + PID生成machineId
     */
    public SnowflakeIdWorker() {
        long datacenterId = getDatacenterId(MAX_DATACENTER_NUM);
        long machineId = getMachineId(datacenterId, MAX_MACHINE_NUM);
        check(datacenterId, machineId);
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }
    /**
     * datacenterId和machineId可配置
     * @param datacenterId
     * @param machineId
     */
    public SnowflakeIdWorker(long datacenterId, long machineId) {
        check(datacenterId, machineId);
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    private static void check(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new RuntimeException(String.format("datacenterId can't be greater than %s or less than 0", MAX_DATACENTER_NUM));
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new RuntimeException(String.format("machineId can't be greater than %s or less than 0", MAX_MACHINE_NUM));
        }
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }
    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     * @return 当前时间戳
     */
    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }
    /**
     * 返回以毫秒为单位的当前时间
     * @return 当前时间(毫秒)
     */
    private long getNewstmp() {
        return System.currentTimeMillis();
    }
    /**
     * 机器标识
     */
    private static long getMachineId(long datacenterId, long maxWorkerId) {
        StringBuilder mpid = new StringBuilder();
        mpid.append(datacenterId);
        String name = ManagementFactory.getRuntimeMXBean().getName();
        if (!name.isEmpty()) {
            /** GET jvmPid */
            mpid.append(name.split("@")[0]);
        }
        /** MAC + PID 的 hashcode 获取16个低位 */
        return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
    }

    /**
     * 数据标识id部分
     */
    private static long getDatacenterId(long maxDatacenterId) {
        long id = 0L;
        try {
            InetAddress ip = InetAddress.getLocalHost();
            NetworkInterface network = NetworkInterface.getByInetAddress(ip);
            if (network == null) {
                id = 1L;
            } else {
                byte[] mac = network.getHardwareAddress();
                id = ((0x000000FF & (long) mac[mac.length - 1])
                        | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
                id = id % (maxDatacenterId + 1);
            }
        } catch (Exception e) {
            logger.error("getDatacenterId exception.", e);
        }
        return id;
    }
}
